In mobile communications, a handoff is an automatic switchover of the current traffic channel that occurs when a mobile terminal moves from one cell to another cell. Such a handoff is typically classified into a hard handoff and a soft handoff. The hard handoff first breaks the existing communication channel before opening a new traffic channel, whereas the soft handoff first connects the new channel and then breaks the existing channel.
In other words, according to the hard handoff procedure, when a mobile communication terminal (i.e., mobile station) moves from one base station to another base station, the channel connected to the existing base station is released, and a new channel of the new base station is then connected. According to the soft handoff procedure, which is a handoff between cells, when a mobile communication terminal (i.e., mobile station) comes near another cell region having the same frequency while the mobile terminal is in use, the mobile terminal detects and informs the current cell that the signal strength of the pilot signal of a new cell is sufficiently high. The new cell then opens a traffic channel for the mobile terminal with the new base station. At this time, the mobile terminal simultaneously maintains communication through the traffic channels of the two cells.
As the mobile terminal approaches the new cell, the signal of the previous cell becomes weaker. If the strength of this previous signal is lower than a predetermined level, the mobile terminal informs the two cells of this fact, and the previous cell breaks the communication channel through the mobile station. The mobile terminal thus continues the call through the new cell having a stronger signal state.
A softer handoff is a handoff between different sectors of one cell. According to the softer handoff, one cell is divided into several sectors, and when the mobile terminal in use moves from one sector to another sector within the same base station, the traffic channel is connected in the same manner as the soft handoff.
Meanwhile, a high-speed data transmitting system may use a code combining soft handoff (CCSH) method using turbo coding. According to the CCSH, one signal is encoded by different coding methods, and resultant coded signals are transmitted. A receiving part decodes and combines the signals encoded by the different coding methods to obtain a gain. According to the CCSH handoff method, several base stations transmit the signals encoded by different coding methods from the various base stations and a mobile terminal receives and combines the signals encoded by the different coding methods to obtain the gain. If the mobile terminal receives the signals encoded by the same coding method, however, it obtains no gain.
For example, as shown in FIG. 1, data to be transmitted to a base station is outputted from a master switch center 101 of a base station controller. The data is then inputted to a turbo encoder 101b, which encodes the data. The turbo encoder 101b then outputs two signals encoded with different patterns.
The two signals are transmitted to the respective base stations with pilot signals from respective pilot channel sections 102a and 102b included therein. The transmitted signals are then received by the mobile terminal from each of the respective base stations. The mobile terminal decodes and combines the two signals encoded with different patterns to obtain the gain.
Meanwhile, according to the CCSH handoff method, the respective base station is allocated with a PN number for discrimination among base stations and cell regions that transmit/receive signals to/from the mobile terminal. In transmitting/receiving the signals to/from the mobile terminal, the respective base stations are under the control of the base station controller, and have different code patterns.
CCSH is a scheme for achieving both coding gain and diversity gain, and has been adopted in a cdma2000 standard for a code division multiple access (CDMA) network. Accordingly, there is a need to apply CCSH to other types of communication technologies to achieve higher gain.